Silicon selective removal

ABSTRACT

A method of etching exposed silicon on patterned heterogeneous structures is described and includes a gas phase etch using plasma effluents formed in a remote plasma. The remote plasma excites a fluorine-containing precursor. Plasma effluents within the remote plasma are flowed into a substrate processing region where the plasma effluents combine with a hydrogen-containing precursor. The combination react with the patterned heterogeneous structures to remove an exposed silicon portion faster than a second exposed portion. The silicon selectivity results from the presence of an ion suppressor positioned between the remote plasma and the substrate processing region. The methods may be used to selectively remove silicon faster than silicon oxide, silicon nitride and a variety of metal-containing materials. The methods may be used to remove small etch amounts in a controlled manner and may result in an extremely smooth silicon surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Prov. Pat. App. No.62/126,873 filed Mar. 2, 2015, and titled “SILICON SELECTIVE REMOVAL” byLi et al., which is hereby incorporated herein in its entirety byreference for all purposes.

FIELD

Embodiments described herein relate to selectively etching silicon.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a pattern in photoresist into underlyinglayers, thinning layers or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess which etches one material faster than another helping e.g. apattern transfer process proceed. Such an etch process is said to beselective of the first material relative to the second material. As aresult of the diversity of materials, circuits and processes, etchprocesses have been developed with a selectivity towards a variety ofmaterials.

Dry etch processes are often desirable for selectively removing materialfrom semiconductor substrates. The desirability stems from the abilityto gently remove material from miniature structures with minimalphysical disturbance. Dry etch processes also allow the etch rate to beabruptly stopped by removing the gas phase reagents. Some dry-etchprocesses involve the exposure of a substrate to remote plasmaby-products formed from one or more precursors.

For example, remote plasma generation of nitrogen trifluoride incombination with ion suppression techniques enables silicon to beselectively removed from a patterned substrate when the plasma effluentsare flowed into the substrate processing region. However, the siliconselectivity occasionally needs to be even higher for certainapplications.

Methods are needed to increase silicon selectively relatively to siliconoxide, silicon nitride and other materials for dry etch processes.

SUMMARY

A method of etching exposed silicon on patterned heterogeneousstructures is described and includes a gas phase etch using plasmaeffluents formed in a remote plasma. The remote plasma excites afluorine-containing precursor. Plasma effluents within the remote plasmaare flowed into a substrate processing region where the plasma effluentscombine with a hydrogen-containing precursor. The combination react withthe patterned heterogeneous structures to remove an exposed siliconportion faster than a second exposed portion. The silicon selectivityresults from the presence of an ion suppressor positioned between theremote plasma and the substrate processing region. The methods may beused to selectively remove silicon faster than silicon oxide, siliconnitride and a variety of metal-containing materials. The methods may beused to remove small etch amounts in a controlled manner and may resultin an extremely smooth silicon surface.

Embodiments disclosed herein include methods of etching a patternedsubstrate. The methods include placing the patterned substrate in asubstrate processing region of a substrate processing chamber. Thepatterned substrate includes an exposed silicon portion and a secondexposed portion. The second exposed portion includes at least oneelement other than silicon. The methods further include flowing afluorine-containing precursor into a remote plasma region fluidlycoupled to the substrate processing region while forming a remote plasmain the remote plasma region to produce plasma effluents. The methodsfurther include flowing a hydrogen-containing precursor into thesubstrate processing region without first passing thehydrogen-containing precursor through the remote plasma region. Themethods further include etching the exposed silicon portion by flowingthe plasma effluents into the substrate processing region. The exposedsilicon portion etches at a first etch rate and the second exposedportion etches at a second etch rate which is lower than the first etchrate.

The first etch rate may exceed the second etch rate by a factor of morethan 80. The substrate processing region may be plasma-free during theoperation of etching the exposed silicon portion. Thehydrogen-containing precursor may not be excited by any plasma outsidethe substrate processing region prior to entering the substrateprocessing region. The fluorine-containing precursor may includes aprecursor selected from the group consisting of atomic fluorine,diatomic fluorine, nitrogen trifluoride, carbon tetrafluoride, hydrogenfluoride and xenon difluoride. The second exposed portion may includesilicon oxide or silicon nitride. The second exposed portion may have anatomic silicon concentration of less than 90% silicon. The exposedsilicon portion may have an atomic silicon concentration of greater than93% silicon. The exposed silicon portion may consist only of silicon.The hydrogen-containing precursor includes at least one of ammonia, ahydrocarbon or molecular hydrogen (H₂).

Embodiments disclosed herein include methods of etching a patternedsubstrate. The methods include placing the patterned substrate in asubstrate processing region of a substrate processing chamber. Thepatterned substrate comprises an exposed silicon portion and a secondexposed portion. The methods further include flowing a radical-fluorineprecursor into the substrate processing region. The methods furtherinclude flowing a hydrogen-containing precursor into the substrateprocessing region without first passing the hydrogen-containingprecursor through any plasma. The methods further include etching theexposed silicon portion.

The exposed silicon portion etches at a first etch rate and the secondexposed portion etches at a second etch rate which is lower than thefirst etch rate during the operation of etching the exposed siliconportion.

Etching the exposed silicon portion may include removing silicon at anetch rate between 1 Å/min and 100 Å/min. Etching the exposed siliconportion may include removing between 5 Å and 30 Å of silicon. Anelectron temperature within the substrate processing region may be below0.5 eV during the operation of etching the exposed silicon portion. Thesecond exposed portion may be an exposed silicon oxide portion and theetch selectivity (silicon:silicon oxide) of the operation of etching theexposed silicon portion may be greater than 100:1. The second exposedportion may be an exposed silicon nitride portion and the etchselectivity (silicon:silicon nitride) of the operation of etching theexposed silicon portion may be greater than 150:1.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the disclosed embodiments. The features andadvantages of the disclosed embodiments may be realized and attained bymeans of the instrumentalities, combinations, and methods described inthe specification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodimentsmay be realized by reference to the remaining portions of thespecification and the drawings.

FIG. 1 is a flow chart of a silicon selective etch process according toembodiments.

FIG. 2 is a flow chart of a silicon selective etch process according toembodiments.

FIG. 3A shows a schematic cross-sectional view of a substrate processingchamber according to embodiments.

FIG. 3B shows a schematic cross-sectional view of a portion of asubstrate processing chamber according to embodiments.

FIG. 3C shows a bottom view of a showerhead according to embodiments.

FIG. 4 shows a top view of an exemplary substrate processing systemaccording to embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

A method of etching exposed silicon on patterned heterogeneousstructures is described and includes a gas phase etch using plasmaeffluents formed in a remote plasma. The remote plasma excites afluorine-containing precursor. Plasma effluents within the remote plasmaare flowed into a substrate processing region where the plasma effluentscombine with a hydrogen-containing precursor. The combination react withthe patterned heterogeneous structures to remove an exposed siliconportion faster than a second exposed portion. The silicon selectivityresults from the presence of an ion suppressor positioned between theremote plasma and the substrate processing region. The methods may beused to selectively remove silicon faster than silicon oxide, siliconnitride and a variety of metal-containing materials. The methods may beused to remove small etch amounts in a controlled manner and may resultin an extremely smooth silicon surface.

Silicon portions are selectively removed in comparison, for example, tosilicon oxide portions or silicon nitride portions when thehydrogen-containing precursor is not excited in any plasma prior toentering the substrate processing region. Only the fluorine-containingprecursor is excited in the remote plasma to form plasma effluentscomprising a radical-fluorine precursor.

Without binding the coverage of the claims to hypothetical mechanismswhich may or may not be entirely correct, the inventors hypothesize thatthe preponderance of unexcited hydrogen-containing precursor (e.g. H₂)maintains a stable hydrogen termination on a broad array of exposedmaterials. The exposure to the unexcited hydrogen-containing precursoralso hydrogen terminates silicon surfaces, however, the fluorineradicals are able to break the Si—H bonds to form Si—F bonds untilvolatile SiF_(x) species desorb from the surface and are evacuated fromthe substrate processing region. The open bonding sites (left behind bythe desorption event) are quickly hydrogen terminated and the processcontinues, especially when the hydrogen-containing precursor is moreplentiful than the radical-fluorine in the substrate processing region.

To better understand and appreciate the embodiments, reference is nowmade to FIG. 1 which is a flow chart of a silicon selective etch process101 according to embodiments. Prior to the first operation, thesubstrate is patterned and an exposed silicon portion is formed on thepatterned substrate. An exposed silicon nitride portion is also formedon the patterned substrate. The patterned substrate is then placedwithin the substrate processing region in operation 110.

Nitrogen trifluoride is flowed into a remote plasma region in operation120. The nitrogen trifluoride is excited in a remote plasma formed inthe remote plasma region (also in operation 120). The remote plasmasystem is positioned next to the substrate processing region and fluidlycoupled through a dual-channel showerhead. A substrate processingchamber may house both the remote plasma region and the substrateprocessing region. The plasma effluents formed in the remote plasma arethen flowed through the dual-channel showerhead into the substrateprocessing region (operation 130). A hydrogen-containing precursor (e.g.H₂) is simultaneously flowed into the substrate processing region andcombined with the plasma effluents in operation 130. Thehydrogen-containing precursor is not passed through the remote plasmaregion and therefore may only be excited by interaction with the plasmaeffluents according to embodiments. The hydrogen-containing precursor isnot passed through any remote plasma region before entering thesubstrate processing region in embodiments. The hydrogen-containingprecursor may be introduced through separate pores in a dual-channelshowerhead into the substrate processing region without prior plasmaexcitation. Generally speaking, the hydrogen-containing precursor mayinclude at least one precursor selected from the group consisting of H₂,NH₃ and hydrocarbons. Other sources of fluorine may be used to augmentor replace the nitrogen trifluoride. In general, a fluorine-containingprecursor is flowed into the remote plasma region and thefluorine-containing precursor comprises at least one precursor selectedfrom the group consisting of atomic fluorine, diatomic fluorine,nitrogen trifluoride, carbon tetrafluoride, hydrogen fluoride and xenondifluoride.

The patterned substrate is selectively etched (operation 140) such thatthe exposed silicon oxide is removed at a very slow rate (5 Å/min) butstill at a much higher rate than the exposed silicon nitride. Thereactive chemical species are removed and the patterned substrate isremoved from the substrate processing region (operation 150). With thedecreasing size of integrated circuits, there is a need to remove eversmaller thicknesses to subtly recess a variety of features. A benefit ofthe low etch rate described herein is that small amounts of silicon maybe reproducibly removed. A further benefit of the low etch rate methodsdescribed herein has been found to include a smoother interface whichalso positively impacts the performance of integrated circuits.

Reference is now made to FIG. 2 which is also a flow chart of a siliconselective etch process 201 according to embodiments. The substrate ispatterned and an exposed silicon portion and an exposed silicon oxideportion are formed on the patterned substrate. The patterned substrateis then placed within the substrate processing region in operation 210.A fluorine-containing precursor (e.g. NF₃) is flowed into a remoteplasma region in operation 220. The fluorine-containing precursor isexcited in a remote plasma formed in the remote plasma region (also inoperation 220). The remote plasma is formed by capacitively applying 5watts of RF power between two parallel plates (one above one below) theremote plasma region (operation 230). The plasma effluents formed in theremote plasma are then flowed through the dual-channel showerhead intothe substrate processing region (operation 240). A hydrogen-containingprecursor (e.g. H₂) is simultaneously flowed into the substrateprocessing region and combined with the plasma effluents in operation240. The patterned substrate is selectively etched (operation 250) suchthat the exposed silicon oxide is selectively removed at a very slowrate but still at a much higher rate than the exposed silicon oxide. Thereactive chemical species are removed and the patterned substrate isremoved from the substrate processing region (operation 260).

The etch processes and process parameters described herein may be usedto smoothly remove silicon at a slow and controlled rate which isincreasingly useful for semiconductor front-end processes. The etchprocess may remove silicon at an etch rate between 1 Å/min and 100Å/min, between 1 Å/min and 50 Å/min, between 1 Å/min and 25 Å/min orbetween 1 Å/min and 15 Å/min in embodiments. The selectivity, thenon-local plasma, the controlled ionic concentration and the lack ofsolid byproducts, each make these etch processes well suited fordelicately removing or trimming silicon structures removing little orsecondary materials. According to embodiments, the etch amount ofsilicon removed in by silicon selective etch process 101 may be between5 Å and 30 Å, between 6 Å and 25 Å or between 7 Å and 20 Å.

The flow of the fluorine-containing precursor may be accompanied by aflow of a relatively inert gas such as one or more of He, N₂ and Ar. Theflow of the hydrogen-containing precursor may also be independentlyaccompanied by a flow of a relatively inert gas as well according toembodiments. Generally speaking inert gases can be used to provide asteadier flow rate of reactive precursor, to improve plasma stabilityand/or to carry liquid precursors to the remote plasma region and/or thesubstrate processing region as appropriate. Flow rates and ratios of theprecursors may be used to control etch rates and etch selectivity asdescribed shortly. In an embodiment, the fluorine-containing gasincludes NF₃ at a flow rate of between 1 sccm (standard cubiccentimeters per minute) and 30 sccm, H₂ at a flow rate of between 500sccm and 5,000 sccm, He at a flow rate of between 0 sccm and 3000 sccm,and Ar at a flow rate of between 0 sccm and 3000 sccm. One of ordinaryskill in the art would recognize that other gases and/or flows may beused depending on a number of factors including processing chamberconfiguration, substrate size, geometry and layout of features beingetched. The flow rate of the fluorine-containing gas may be less than 30sccm, less than 20 sccm, less than 15 sccm or less than 10 sccmaccording to embodiments. Lower flow rates of the fluorine-containinggas may increase the silicon selectivity in embodiments. The flow rateof the hydrogen-containing gas may be greater than 300 sccm, greaterthan 500 sccm, greater than 1000 sccm or greater than 2000 sccm inembodiments. Increasing the flow rate of the inert gas also desirablylowers the silicon etch rate, increasing control for small etch amounts.The flow rate of the inert gas (e.g. argon) may be greater than 1,000sccm, greater than 2,000 sccm, greater than 4,000 sccm or greater than10,000 sccm according to embodiments.

The flow rate of the nitrogen trifluoride may be low relative to theflow rate of the hydrogen to effect an atomic flow ratio H:F abovethreshold levels in embodiments. Atomic flow ratios above thesethresholds may be used to help achieve high etch selectivity of silicon,according to embodiments, to attain the high etch selectivities reportedherein. The atomic flow ratio H:F may be greater than one (i.e. >1:1),greater than 2:1 or greater than 4:1 in embodiments. These rangesrepresent considerably broader process windows than previouslyavailable. Higher atomic flow ratios H:F may increase the siliconselectivity in embodiments. Some precursors may contain both fluorineand hydrogen, in which case the atomic flow rate of all contributionsare included when calculating the atomic flow ratio described herein.The atomic flow ratio Ar:F (or another inert gas) may be greater than100:1, greater than 150:1 or greater than 200:1 in embodiments.

The methods presented herein exhibit high etch selectivity of theexposed silicon portion relative to an exposed silicon nitride and/orsilicon oxide portions. The etch selectivity (silicon:silicon oxide) maybe greater than 100:1, greater than 150:1, greater than 200:1 or greaterthan 250:1 in embodiments. The etch selectivity (silicon:siliconnitride) may be greater than 150:1, greater than 200:1, greater than250:1 or greater than 300:1 in embodiments.

Without binding the claim coverage to hypothetical mechanisms, thepreponderance of hydrogen may hydrogen terminate exposed surfaces on thepatterned substrate. Hydrogen termination may be metastable on theexposed silicon portions. Fluorine from the nitrogen trifluoride orother fluorine-containing precursor may be displacing the hydrogen onthe silicon surface and create volatile residue which leaves the surfaceand carries silicon away. Due to the strong bond energies present in theother exposed materials, the fluorine may be unable to displace thehydrogen of the other hydrogen terminated surfaces (and/or may be unableto create volatile residue to remove the other exposed material).

Increasing the flow rate of the hydrogen-containing gas generallyincreases silicon selectivity. The atomic flow ratio H:F may bemaintained at the higher levels indicated herein to reduce or eliminatesolid residue formation on silicon oxide. The formation of solid residuemay consume silicon oxide which may reduce the silicon selectivity ofthe etch process. Lower flow rates of the fluorine-containing gas mayincrease the silicon selectivity.

Generally speaking, the methods presented herein may be used toselectively etch silicon relative to a wide variety of materials and notjust silicon oxide and/or silicon nitride. The methods may also be usedto selectively etch exposed silicon (in the form of single crystalsilicon, polysilicon or amorphous silicon) faster than titanium,titanium nitride, titanium oxide, titanium silicide, hafnium, hafniumoxide, hafnium silicide, tantalum, tantalum oxide, tantalum nitride,tantalum silicide, cobalt, cobalt oxide, cobalt silicide, tungsten,tungsten oxide, tungsten silicide, silicon carbide, silicon oxynitride,silicon carbon nitride, C—H films, C—H—N films, silicon germanium,germanium, nickel, nickel oxide or nickel silicide. The first etch ratemay be used to describe the etch rate of the exposed silicon portion andthe second etch rate may be used to describe the etch rate of the secondexposed portion of the alternative material. The first etch rate mayexceed the second etch rate by a factor of more than 80, more than 120or more than 150 in embodiments. The second exposed portion may have acompositional atomic ratio other than 100% Si which includes all theexemplary alternative materials listed above and further specifiedbelow. The second exposed portion may have an atomic siliconconcentration less than 90%, less than 80% or less than 70% according toembodiments. The exposed silicon portion may have an atomic siliconconcentration greater than 90%, greater than 95% or greater than 97% inembodiments. The exposed silicon portion may consist of siliconaccording to embodiments. In one example, metal-containing portions mayalso be present on the patterned substrate, such as the tantalum cobalt,tungsten, hafnium, or titanium-containing examples just given. The etchrate ratio (the etch selectivity silicon:exposed metal-containingportion) may be greater than 100:1, greater than 150:1, greater than200:1, greater than 250:1, greater than 500:1, greater than 1000:1,greater than 2000:1 or greater than 3000:1 in embodiments.

The high etch selectivities described herein may be assisted by makingthe hydrogen-containing precursor devoid or essentially devoid ofoxygen. Similarly, the remote plasma region and the substrate processingregion may be described as oxygen-free or devoid of oxygen, inembodiments, during silicon selective etch process 101, siliconselective etch process 201, operation 140, and/or operation 250. Thefluorine-containing precursor may be devoid of essentially devoid ofoxygen, as well, according to embodiments.

The second exposed portion may include at least one element from thegroup consisting of nitrogen, hafnium, titanium, cobalt, carbon,tantalum, tungsten, and germanium according to embodiments. The secondexposed portion may consist essentially of or consist of a compositionselected from the group of tantalum, tantalum and oxygen, tantalum andsilicon, tantalum and nitrogen, cobalt, cobalt and oxygen, cobalt andsilicon, tungsten, tungsten and oxygen, tungsten and silicon, nickel,nickel and oxygen, nickel and silicon, silicon and nitrogen, silicon andoxygen and nitrogen, silicon and carbon and nitrogen, silicon andcarbon, carbon, carbon and hydrogen, carbon and hydrogen and nitrogen,silicon and germanium, germanium, hafnium, hafnium and oxygen, hafniumand silicon, titanium, titanium and oxygen, titanium and nitrogen, ortitanium and silicon in embodiments.

The pressure in the substrate processing region and the remote plasmaregion(s) during the etching operations may be between 0.01 Ton and 50Ton, between 0.1 Torr and 15 Torr or between 0.2 Torr and 10 Torr inembodiments. The temperature of the patterned substrate during theetching operations may be between −40° C. and 250° C., between −30° C.and 150° C. or between −20° C. and 50° C. in embodiments. Lowerpatterned substrate temperatures correlate with a smoother post-etchsurface. The temperature of the patterned substrate during the etchingoperations may be between 100° C. and 400° C., between 150° C. and 350°C. or between 200° C. and 300° C. in embodiments. Higher patternedsubstrate temperatures correlated with a reduced etch rate and greatercontrol of etch amount.

The method also includes applying power to the fluorine-containingprecursor during operations 120 and 220 in the remote plasma regions togenerate the plasma effluents. The plasma parameters described hereinapply to remote plasmas used to etch the patterned substrate. As wouldbe appreciated by one of ordinary skill in the art, the plasma mayinclude a number of charged and neutral species including radicals andions. The plasma may be generated using known techniques (e.g., RF,capacitively coupled, inductively coupled). In an embodiment, the remoteplasma power may be applied to the remote plasma region at a levelbetween 500 W and 10 kW for a remote plasma external to the substrateprocessing chamber. The remote plasma power may be applied usinginductive coils, in embodiments, in which case the remote plasma will bereferred to as an inductively-coupled plasma (ICP) or may be appliedusing capacitive plates, in which case the remote plasma will bereferred to as a capacitive-coupled plasma (CCP). According toembodiments, the remote plasma power may be applied to the remote plasmaregion at a level between 3 watts and 2000 watts, between 5 watts and500 watts or between 5 watts and 150 watts for a remote plasma withinthe substrate processing chamber. Other possible plasma parameters andranges will be described along with exemplary equipment herein.

For both treatment remote plasmas and etch remote plasmas, the flows ofthe precursors into the remote plasma region may further include one ormore relatively inert gases such as He, N₂, Ar. The inert gas can beused to improve plasma stability, ease plasma initiation, and improveprocess uniformity. Argon may be helpful, as an additive, to promote theformation of a stable plasma. Process uniformity is generally increasedwhen helium is included. These additives are present in embodimentsthroughout this specification regardless of whether the accompanyingprecursor is flowed through a remote plasma or directly into thesubstrate processing region. Flow rates and ratios of the precursors maybe used to control etch rates and etch selectivity.

In embodiments, an ion suppressor (which may be the showerhead) may beused to provide radical and/or neutral species for gas-phase etching.The ion suppressor may also be referred to as an ion suppressionelement. In embodiments, for example, the ion suppressor is used tofilter etching plasma effluents en route from the remote plasma regionto the substrate processing region. The ion suppressor may be used toprovide a reactive gas having a higher concentration of radicals thanions. Plasma effluents pass through the ion suppressor disposed betweenthe remote plasma region and the substrate processing region. The ionsuppressor functions to dramatically reduce or substantially eliminateionic species traveling from the plasma generation region to thesubstrate. The ion suppressors described herein are simply one way toachieve a low electron temperature in the substrate processing regionduring the gas-phase etch processes described herein.

In embodiments, an electron beam is passed through the substrateprocessing region in a plane parallel to the substrate to reduce theelectron temperature of the plasma effluents. A simpler showerhead maybe used if an electron beam is applied in this manner. The electron beammay be passed as a laminar sheet disposed above the substrate inembodiments. The electron beam provides a source of neutralizingnegative charge and provides a more active means for reducing the flowof positively charged ions towards the substrate and increasing the etchselectivity in embodiments. The flow of plasma effluents and variousparameters governing the operation of the electron beam may be adjustedto lower the electron temperature measured in the substrate processingregion.

The electron temperature may be measured using a Langmuir probe in thesubstrate processing region during excitation of a plasma in the remoteplasma. In embodiments, the electron temperature may be less than 0.5eV, less than 0.45 eV, less than 0.4 eV, or less than 0.35 eV during theetching operations. These extremely low values for the electrontemperature are enabled by the presence of the electron beam, showerheadand/or the ion suppressor. Uncharged neutral and radical species maypass through the electron beam and/or the openings in the ion suppressorto react at the substrate. Such a process using radicals and otherneutral species can reduce plasma damage compared to conventional plasmaetch processes that include sputtering and bombardment. Embodimentsdescribed are also advantageous over conventional wet etch processeswhere surface tension of liquids can cause bending and peeling of smallfeatures. In point of contrast, the electron temperature during theselective etch process may be greater than 0.5 eV, greater than 0.6 eVor greater than 0.7 eV according to embodiments.

The substrate processing region may be described herein as “plasma-free”during the etch processes described herein. “Plasma-free” does notnecessarily mean the region is devoid of plasma. Ionized species andfree electrons created within the plasma region may travel through pores(apertures) in the partition (showerhead) at exceedingly smallconcentrations. The borders of the plasma in the chamber plasma regionmay encroach to some small degree upon the substrate processing regionthrough the apertures in the showerhead. Furthermore, a low intensityplasma may be created in the substrate processing region withouteliminating desirable features of the etch processes described herein.All causes for a plasma having much lower intensity ion density than thechamber plasma region during the creation of the excited plasmaeffluents do not deviate from the scope of “plasma-free” as used herein.

FIG. 3A shows a cross-sectional view of an exemplary substrateprocessing chamber 1001 with a partitioned plasma generation regionwithin the processing chamber. During film etching, a process gas may beflowed into chamber plasma region 1015 through a gas inlet assembly1005. A remote plasma system (RPS) 1002 may optionally be included inthe system, and may process a first gas which then travels through gasinlet assembly 1005. The process gas may be excited within RPS 1002prior to entering chamber plasma region 1015. Accordingly, thefluorine-containing precursor as discussed above, for example, may passthrough RPS 1002 or bypass the RPS unit in embodiments.

A cooling plate 1003, faceplate 1017, ion suppressor 1023, showerhead1025, and a substrate support 1065 (also known as a pedestal), having asubstrate 1055 disposed thereon, are shown and may each be includedaccording to embodiments. Pedestal 1065 may have a heat exchange channelthrough which a heat exchange fluid flows to control the temperature ofthe substrate. This configuration may allow the substrate 1055temperature to be cooled or heated to maintain relatively lowtemperatures, such as between −40° C. to 200° C. Pedestal 1065 may alsobe resistively heated to relatively high temperatures, such as between100° C. and 1100° C., using an embedded heater element.

Exemplary configurations may include having the gas inlet assembly 1005open into a gas supply region 1058 partitioned from the chamber plasmaregion 1015 by faceplate 1017 so that the gases/species flow through theholes in the faceplate 1017 into the chamber plasma region 1015.Structural and operational features may be selected to preventsignificant backflow of plasma from the chamber plasma region 1015 backinto the supply region 1058, gas inlet assembly 1005, and fluid supplysystem 1010. The structural features may include the selection ofdimensions and cross-sectional geometries of the apertures in faceplate1017 to deactivate back-streaming plasma. The operational features mayinclude maintaining a pressure difference between the gas supply region1058 and chamber plasma region 1015 that maintains a unidirectional flowof plasma through the showerhead 1025. The faceplate 1017, or aconductive top portion of the chamber, and showerhead 1025 are shownwith an insulating ring 1020 located between the features, which allowsan AC potential to be applied to the faceplate 1017 relative toshowerhead 1025 and/or ion suppressor 1023. The insulating ring 1020 maybe positioned between the faceplate 1017 and the showerhead 1025 and/orion suppressor 1023 enabling a capacitively coupled plasma (CCP) to beformed in the chamber plasma region.

The plurality of holes in the ion suppressor 1023 may be configured tocontrol the passage of the activated gas, i.e., the ionic, radical,and/or neutral species, through the ion suppressor 1023. For example,the aspect ratio of the holes, or the hole diameter to length, and/orthe geometry of the holes may be controlled so that the flow ofionically-charged species in the activated gas passing through the ionsuppressor 1023 is reduced. The holes in the ion suppressor 1023 mayinclude a tapered portion that faces chamber plasma region 1015, and acylindrical portion that faces the showerhead 1025. The cylindricalportion may be shaped and dimensioned to control the flow of ionicspecies passing to the showerhead 1025. An adjustable electrical biasmay also be applied to the ion suppressor 1023 as an additional means tocontrol the flow of ionic species through the suppressor. The ionsuppression element 1023 may function to reduce or eliminate the amountof ionically charged species traveling from the plasma generation regionto the substrate. Uncharged neutral and radical species may still passthrough the openings in the ion suppressor to react with the substrate.

Plasma power can be of a variety of frequencies or a combination ofmultiple frequencies. In the exemplary processing system the plasma maybe provided by RF power delivered to faceplate 1017 relative to ionsuppressor 1023 and/or showerhead 1025. The RF power may be between 10watts and 5000 watts, between 100 watts and 2000 watts, between 200watts and 1500 watts, or between 200 watts and 1000 watts inembodiments. The RF frequency applied in the exemplary processing systemmay be low RF frequencies less than 200 kHz, high RF frequencies between10 MHz and 15 MHz, or microwave frequencies greater than 1 GHz inembodiments. The plasma power may be capacitively-coupled (CCP) orinductively-coupled (ICP) into the remote plasma region.

A precursor, for example a fluorine-containing precursor, may be flowedinto substrate processing region 1033 by embodiments of the showerheaddescribed herein. Excited species derived from the process gas inchamber plasma region 1015 may travel through apertures in the ionsuppressor 1023, and/or showerhead 1025 and react with ahydrogen-containing precursor flowing into substrate processing region1033 from a separate portion of the showerhead, which may therefore becalled a dual-channel showerhead. Little or no plasma may be present insubstrate processing region 1033 during the remote plasma etch process.Excited derivatives of the precursors may combine in the region abovethe substrate and/or on the substrate to etch structures or removespecies from the substrate.

The processing gases may be excited in chamber plasma region 1015 andmay be passed through the showerhead 1025 to substrate processing region1033 in the excited state. While a plasma may be generated in substrateprocessing region 1033, a plasma may alternatively not be generated inthe processing region. In one example, the only excitation of theprocessing gas or precursors may be from exciting the processing gasesin chamber plasma region 1015 to react with one another in substrateprocessing region 1033. As previously discussed, this may be to protectthe structures patterned on substrate 1055.

FIG. 3B shows a detailed view of the features affecting the processinggas distribution through faceplate 1017. The gas distribution assembliessuch as showerhead 1025 for use in the processing chamber section 1001may be referred to as dual-channel showerheads (DCSH) and areadditionally detailed in the embodiments described in FIG. 3A as well asFIG. 3C herein. The dual channel showerhead may provide for etchingprocesses that allow for separation of etchants outside of theprocessing region 1033 to provide limited interaction with chambercomponents and each other prior to being delivered into the processingregion.

The showerhead 1025 may comprise an upper plate 1014 and a lower plate1016. The plates may be coupled with one another to define a volume 1018between the plates. The coupling of the plates may be so as to providefirst fluid channels 1019 through the upper and lower plates, and secondfluid channels 1021 through the lower plate 1016. The formed channelsmay be configured to provide fluid access from the volume 1018 throughthe lower plate 1016 via second fluid channels 1021 alone, and the firstfluid channels 1019 may be fluidly isolated from the volume 1018 betweenthe plates and the second fluid channels 1021. The volume 1018 may befluidly accessible through a side of the gas distribution assembly 1025.Although the exemplary system of FIGS. 3A-3C includes a dual-channelshowerhead, it is understood that alternative distribution assembliesmay be utilized that maintain first and second precursors fluidlyisolated prior to substrate processing region 1033. For example, aperforated plate and tubes underneath the plate may be utilized,although other configurations may operate with reduced efficiency or notprovide as uniform processing as the dual-channel showerhead described.

In the embodiment shown, showerhead 1025 may distribute via first fluidchannels 1019 process gases which contain plasma effluents uponexcitation by a plasma in chamber plasma region 1015. In embodiments,the process gas introduced into RPS 1002 and/or chamber plasma region1015 may contain fluorine, e.g., NF₃. The process gas may also include acarrier gas such as helium, argon, nitrogen (N₂), etc. Plasma effluentsmay include ionized or neutral derivatives of the process gas and mayalso be referred to herein as a radical-fluorine precursor referring tothe atomic constituent of the process gas introduced.

FIG. 3C is a bottom view of a showerhead 1025 for use with a processingchamber in embodiments. Showerhead 1025 corresponds with the showerheadshown in FIG. 3A. Through-holes 1031, which show a view of first fluidchannels 1019, may have a plurality of shapes and configurations tocontrol and affect the flow of precursors through the showerhead 1025.Small holes 1027, which show a view of second fluid channels 1021, maybe distributed substantially evenly over the surface of the showerhead,even amongst the through-holes 1031, which may help to provide more evenmixing of the precursors as they exit the showerhead than otherconfigurations.

The chamber plasma region 1015 or a region in an RPS may be referred toas a remote plasma region. In embodiments, the radical-fluorineprecursor is created in the remote plasma region and travel into thesubstrate processing region to combine with the hydrogen-containingprecursor. In embodiments, the hydrogen-containing precursor is excitedonly by the radical-fluorine precursor. Plasma power may essentially beapplied only to the remote plasma region in embodiments to ensure thatthe radical-fluorine precursor provides the dominant excitation.

Embodiments of the dry etch systems may be incorporated into largerfabrication systems for producing integrated circuit chips. FIG. 4 showsone such processing system (mainframe) 1101 of deposition, etching,baking, and curing chambers in embodiments. In the figure, a pair offront opening unified pods (load lock chambers 1102) supply substratesof a variety of sizes that are received by robotic arms 1104 and placedinto a low pressure holding area 1106 before being placed into one ofthe substrate processing chambers 1108 a-f. A second robotic arm 1110may be used to transport the substrate wafers from the holding area 1106to the substrate processing chambers 1108 a-f and back. Each substrateprocessing chamber 1108 a-f, can be outfitted to perform a number ofsubstrate processing operations including the dry etch processesdescribed herein in addition to cyclical layer deposition (CLD), atomiclayer deposition (ALD), chemical vapor deposition (CVD), physical vapordeposition (PVD), etch, pre-clean, degas, orientation, and othersubstrate processes.

The showerhead may be referred to as a dual-channel showerhead as aresult of the two distinct pathways into the substrate processingregion. The fluorine-containing precursor may be flowed through thethrough-holes in the dual-channel showerhead and the hydrogen-containingprecursor may pass through separate channels in the dual-channelshowerhead. The separate channels may open into the substrate processingregion but not into the remote plasma region as described above.

Combined flow rates of plasma effluents and other precursors into thesubstrate processing region may account for 0.05% to 20% by volume ofthe overall gas mixture; the remainder being carrier gases. Thefluorine-containing precursor are flowed into the remote plasma regionbut the plasma effluents have the same volumetric flow ratio, inembodiments. In the case of the fluorine-containing precursor, a purgeor carrier gas may be first initiated into the remote plasma regionbefore the fluorine-containing gas to stabilize the pressure within theremote plasma region.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon” of the patternedsubstrate is predominantly silicon but may include concentrations ofother elemental constituents such as, e.g., nitrogen, oxygen, hydrogenand carbon. In some embodiments, silicon portions etched using themethods described herein consist of or consist essentially of silicon.Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂but may include concentrations of other elemental constituents such as,e.g., nitrogen, hydrogen and carbon. In some embodiments, silicon oxideportions described herein consist of or consist essentially of siliconand oxygen. Exposed “silicon nitride” of the patterned substrate ispredominantly Si₃N₄ but may include concentrations of other elementalconstituents such as, e.g., oxygen, hydrogen and carbon. In someembodiments, silicon nitride portions described herein consist of orconsist essentially of silicon and nitrogen. Exposed “Hafnium oxide” ofthe patterned substrate is predominantly hafnium and oxygen but mayinclude small concentrations of elements other than hafnium and oxygen.In some embodiments, hafnium oxide portions described herein consist ofor consist essentially of hafnium and oxygen. Exposed “Tungsten” of thepatterned substrate is predominantly tungsten but may include smallconcentrations of elements other than tungsten. In some embodiments,tungsten portions described herein consist of or consist essentially oftungsten. Analogous definitions apply to all materials described herein.

The term “gap” is used throughout with no implication that the etchedgeometry has a large horizontal aspect ratio. Viewed from above thesurface, gaps may appear circular, oval, polygonal, rectangular, or avariety of other shapes. A “trench” is a long gap. A trench may be inthe shape of a moat around an island of material whose aspect ratio isthe length or circumference of the moat divided by the width of themoat. The term “via” is used to refer to a low aspect ratio trench (asviewed from above) which may or may not be filled with metal to form avertical electrical connection. As used herein, a conformal etch processrefers to a generally uniform removal of material on a surface in thesame shape as the surface, i.e., the surface of the etched layer and thepre-etch surface are generally parallel. A person having ordinary skillin the art will recognize that the etched interface likely cannot be100% conformal and thus the term “generally” allows for acceptabletolerances.

The term “precursor” is used to refer to any process gas which takespart in a reaction to either remove material from or deposit materialonto a surface. “Plasma effluents” describe gas exiting from the chamberplasma region and entering the substrate processing region. Plasmaeffluents are in an “excited state” wherein at least some of the gasmolecules are in vibrationally-excited, dissociated and/or ionizedstates. A “radical precursor” is used to describe plasma effluents (agas in an excited state which is exiting a plasma) which participate ina reaction to either remove material from or deposit material on asurface. “Radical-fluorine precursors” describe radical precursors whichcontain fluorine but may contain other elemental constituents. Thephrase “inert gas” refers to any gas which does not form chemical bondswhen etching or being incorporated into a film. Exemplary inert gasesinclude noble gases but may include other gases so long as no chemicalbonds are formed when (typically) trace amounts are trapped in a film.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well-known processesand elements have not been described to avoid unnecessarily obscuringthe present embodiments. Accordingly, the above description should notbe taken as limiting the scope of the claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the embodiments, subject to any specifically excluded limit inthe stated range. Where the stated range includes one or both of thelimits, ranges excluding either or both of those included limits arealso included.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A method of etching a patterned substrate, the method comprising:placing the patterned substrate in a substrate processing region of asubstrate processing chamber, wherein the patterned substrate comprisesan exposed silicon portion and a second exposed portion and wherein thesecond exposed portion comprises at least one element other thansilicon; producing plasma effluents by flowing a fluorine-containingprecursor into a remote plasma region fluidly coupled to the substrateprocessing region while forming a remote plasma in the remote plasmaregion; flowing a hydrogen-containing precursor into the substrateprocessing region without first passing the hydrogen-containingprecursor through the remote plasma region; and etching the exposedsilicon portion by flowing the plasma effluents into the substrateprocessing region, wherein the exposed silicon portion etches at a firstetch rate and the second exposed portion etches at a second etch ratewhich is lower than the first etch rate.
 2. The method of claim 1wherein the first etch rate exceeds the second etch rate by a factor ofmore than
 80. 3. The method of claim 1 wherein the substrate processingregion is plasma-free during the operation of etching the exposedsilicon portion.
 4. The method of claim 1 wherein thehydrogen-containing precursor is not excited by any plasma outside thesubstrate processing region prior to entering the substrate processingregion.
 5. The method of claim 1 wherein the fluorine-containingprecursor comprises a precursor selected from the group consisting ofatomic fluorine, diatomic fluorine, nitrogen trifluoride, carbontetrafluoride, hydrogen fluoride and xenon difluoride.
 6. The method ofclaim 1 wherein the second exposed portion comprises silicon oxide orsilicon nitride.
 7. The method of claim 1 wherein the second exposedportion has an atomic silicon concentration of less than 90% silicon. 8.The method of claim 1 wherein the exposed silicon portion has an atomicsilicon concentration of greater than 93% silicon.
 9. The method ofclaim 1 wherein the exposed silicon portion consists of silicon.
 10. Themethod of claim 1 wherein the hydrogen-containing precursor comprises atleast one of ammonia, a hydrocarbon or molecular hydrogen (H₂).
 11. Amethod of etching a patterned substrate, the method comprising: placingthe patterned substrate in a substrate processing region of a substrateprocessing chamber, wherein the patterned substrate has an exposedsilicon portion and a second exposed portion; flowing a radical-fluorineprecursor into the substrate processing region; flowing ahydrogen-containing precursor into the substrate processing regionwithout first passing the hydrogen-containing precursor through anyplasma; etching the exposed silicon portion, wherein the exposed siliconportion etches at a first etch rate and the second exposed portionetches at a second etch rate which is lower than the first etch rate.12. The method of claim 11 wherein etching the exposed silicon portioncomprises removing silicon at an etch rate between 1 Å/min and 100Å/min.
 13. The method of claim 11 wherein etching the exposed siliconportion comprises removing between 5 Å and 30 Å of silicon.
 14. Themethod of claim 11 wherein an electron temperature within the substrateprocessing region is below 0.5 eV during the operation of etching theexposed silicon portion.
 15. The method of claim 1 the second exposedportion is an exposed silicon oxide portion and the etch selectivity(silicon:silicon oxide) of the operation of etching the exposed siliconportion is greater than 100:1.
 16. The method of claim 1 the secondexposed portion is an exposed silicon nitride portion and the etchselectivity (silicon:silicon nitride) of the operation of etching theexposed silicon portion is greater than 150:1.